Liquid level responsive means



n w & mm. H. T. SPARROW 2,304,211

LIQUID LEVEL REsPrJNsIvE MEANS Filed Aug. 31, 1939 3S i bag? 1 Qmaentor Huberl' T. Eparrcw- (Ritorngg iii T. Sow, Minneapolis, Minn., asslgnor to canons-Honeywell Regulator Company, eapolis, Mi a. corporation of Delaware Application August 31, 1939, Serial No. 292,898

9 Claims.

The present invention relates to a liquid level responsive means and more particularly to one employing a thermo-couple as a liquid responsive element.

object of the present invention is to provide an improved type of liquid level responsive means of the heat responsive type which is inherently compensated for ambient temperatures.

A further object of the present invention is to provide a liquid level responsive means employing a thermo-couple which is heated and one junction of which is so located that when the liquid in question is above a predetermined level, the heat is carried away therefrom so that the thermo-couple junctions are at difierent temperatures.

A further object of the present invention is to provide a liquid level responsive means of the type set forth above in which the thermo-couple is formed of a tube adapted to project into the liquid container and a rod within the tube joined thereto to form one junction of the thermocouple.

A further object of the present invention is to provide a liquid responsive means such as set forth in the preceding object in which a heater surrounds the rod intermittent the ends thereof.

A still further object of the present invention is to provide such a liquid level responsive means in connection with a boiler control so that the boiler is operated in accordance with the level of the liquid.

Other objects of the present invention will be apparent from a consideration of the accompanying specification, claims and drawing.

In the single figure of the drawing, the present invention is shown in connection with a boiler, only a portion of the boiler being shown.

Referring specifically to the drawing, the wall of a boiler is designated by the reference numeral it and the liquid therein by the reference numeral ll. It is to be understood that the boiler II! is of any conventional type and the to do this in order to prevent the boiler from being subjected to excessive temperatures such as arises when the water is completely vaporized. The present invention is specifically concerned with a liquid level responsive means adapted to control the boiler to perform any desired control operation such as shutting 05 the burner and opening'a water valve.

Extending through the wall I0 of the boiler is a tube l4. The tube 14 is threadedly secured at l5 to the wall It and has its inner end closed as indicated at l6. Extending concentrically within the tube I6 is a rod like element H. The rod like element I1 is secured at its inner end l8 to the closed end It of tube M by welding or in some other similar fashion. The rod ll forms with the tube l4 a thermo-couple, the materials of rod I1 and tube l4 being selected for their dissimilar thermoelectric characteristics. Thus the tube It may be formed of copper and the tube ll of Constantan, an alloy of about 50% nickel and 50% copper. Welded to the outer end of rod I! is a copper rod 20. The rods I1 and 20 are joined at 2| and this junction constitutes a second junction of the thermo-couple. The interior of the outer end of tube I4 is recessed to provide a shoulder 22 and located within this recessed area against the shoulder 22 is an insulating bar 23 which is provided with a plurality of apertures through one of which rod 20 extends. The bar 23 is held in position by a split spring ring 24 which fits into a groove 25. The bar 23 is of such shape that it only partially closes the open end of tube I4 so that the interior of the tube is exposed to the atmosphere.

Surrounding the rod H at a point slightly closer to junction l8 than to junction 2| is an electrical heating coil, 25, this coil being wound upon a suitable insulating bobbin 21. Extending from the coil are conductors 28 and 29 which extend through apertures in the insulating bar The thermo-couple is provided with'two terminal screws 3| and 32, one being secured to tube l4 and the other to the copper rod 20, The thermo-couple is designed to control the energization of a relay generally designated by the reference numeral 35. This relay comprises a relay coil 36 associated with a switch blade 31. Switch blade 31 is designed to engage either of two contacts 38 or 39. Switch blade 31 is biased 4| and 42 may lead to a burner control and a v Operation of apparatus The various elements are shown in the position they assume when the liquid in the boiler is above the desired level. In this position, the heating coil 26 is supplying heat to both junctions i8 and 2|. By reason of the fact, however, that junction I8 is immersed in the liquid N, the heat supplied to this junction is largely carried away so that this junction remains at a temperature only slightly higher than that of the liquid The junction 2|, on the other hand, is raised to a considerably higher temperature by reason of the heating eiiect of coil 26. It will be noted that the temperature difference between junctions 2| and I8 is relatively independent of ambient temperature since the ambient temperature affects both junctions 2| and I8 substantially the same. Under the conditions just disclosed, the junction 2| is at a temperature which is much higher than that of junction It so that sufficient electromotive force is generated by the thermo-couple to energize the relay 36. Under these conditions the relay switch blade 31 is held in the position shown in which position it is in engagement with contact 38. If contact 38 is used to control the energization of the burner, the burner is maintained in operation when the switch blade is in this position pro vided that the other controls of the system are also calling for burner operation.

If at any time the water level falls below the level of junction l8 and particularly below the tube M, the temperature of junction l8 very quickly rises since the heat is no longer carried away therefrom. By reason of the fact that the heater 2B is located closer to junction |B than to junction 2|, this rise in temperature of junction I8 is quite rapid. The result is that the two junctions 2| and I8 are very quickly at the same temperature so that the relay coil 36 is completely deenergized. Under these circumstances the switch blade 31 is released to move to its biased position in which it is in engagement with contact 39. If contact 391s, for example, used to control the energization of the water valve, the water valve is energized under these circumstances to admit water to the boiler. As soon as the water level again rises above the level of junction l8, the temperature of this junction is again reduced so that junction 2| again becomes the hot junction. The relay coil 36 is then reenergized to cause switch blade 31 to assume again the position shown in the drawing.

It will be noted that the present invention provides a liquid level responsive means of the heat responsive type which is extremely simple in construction and which is relatively free from the effect of ambient temperature. While a specific embodiment of the invention has been shown for purposes of illustration, it is to be understood that the invention is limited only by the scope of the appended claims.

I claim as my invention:

1. In combination, a liquid container, 2. thermocouple comprising a tube of a first material having a closed end projecting into said container, a rod of a material having difierent thermoelectric properties than said first material, said rod being located within said tube and secured at its inner end to the closed end of said tube to form a first junction of said thermocouple, a conductor secured to said rod to form a second junction of said thermocouple, a heater for heating said rod intermediate the ends thereof whereby the relative temperatures of the thermocouple junctions are dependent upon whether the liquid level is suificiently high to immerse said first junction and carry the heat away therefrom, and translating means responsive to the electromotive force generated by said thermocouple.

2. In combination, a boiler, a thermocouple having a first junction projecting into the liquid in said boiler and a second junction not in said liquid, means for heating both junctions of the thermocouple whereby the relative temperatures of the thermocouple junctions are dependent upon whether the liquid level is sufiiciently high to immerse said first junction and carry the heat away therefrom, the heat not being carried away therefrom by the surrounding medium when said first junction is not immersed by said liquid, and means responsive to the electromotive force generated by said thermocouple for controlling said boiler.

3. In combination, a boiler, a thermocouple comprising a tube of a first material having a closed and projecting into said boiler and an open end exposed to the atmosphere, a rod of a material having different thermoelectric properties than said first material, said rod being located within said tube and secured at its inner end to the closed end of said tube to form a first junction of said thermocouple, a conductor secured to said rod to form a second junction of said thermocouple, a heater within the tube intermediate the ends of the rod for heating the junctions of said thermocouple whereby the relative temperatures of the thermocouple junctions are dependent upon whether the liquid level is sumciently high to immerse said first junction and carry the heat therefrom, and means responsive to the electromotive force generated by said thermocouple for controlling said boiler.

4. In combination, a boiler, a thermocouple comprising a tube of a first material having a closed end projecting into said boiler and an open end exposed to the atmosphere, a rod of a material having difl'erent thermo-electric prop erties than said first material, said rod being located within said tube and secured at its inner end to the closed end of said tube to form a first junction of said thermocouple, a conductor secured to said rod to form a second junction of said thermocouple, a heater surrounding the rod intermediate the ends thereof for heating the junctions of said thermocouple whereby the relative temperatures of the thermocouple junctions are dependent upon whether the liquid level is sufficiently high to immerse said first junction and carry the heat therefrom, and means responsive to the electromotive force generated by said thermocouple for controlling said boiler.

5. In combination, a boiler containing a liquid, a tubular member extending into said boiler and having a portion extending slightly below the normal liquid level therein, a rod of a material having different thermo-electric properties than said tubular member, said rod being located within said tubular member and secured to said member at said portion to form a first thermocouple junction, a conductor secured to said rod to form a second thermocouple junction, heating means tending to heat said junctions to substantially the same temperature, said first junction being normally cooled by the liquid in said boiler when the liquid level is normal to thereby cause a temperature differential between said junctions, and translating means responsive to the electromotive force generated by said thermocouple junctions.

6. In a liquid level control, in combination, a thermocouple comprising first and second junctions, means for heating said junctions to substantially the same temperature, means for cooling substantially only one of said junctions in response to a predetermined liquid level to create a temperature differential therebetween to cause an electromotive force to be generated thereby, and translating means responsive to the electromotive force generated by said thermocouple for controlling said liquid level.

7. In combination, a liquid container, a thermocouple having first and second junctions, means for heating said junctions, one of said junctions being so located that when the liquid is above a predetermined normal level the heat is carried away therefrom to cause said thermocouple to generate an electromotive force, the heat not being carried away from said one junction by the medium surrounding said thermocouple when the liquid level is below said normal level, and translating means responsive to the electromotive force generated by said thermocouple.

8. In combination, a boiler, a thermocouple having first and second junctions, means for heating said junctions, one of said junctions being so located that when the boiler liquid is above a predetermined normal level the heat is carried away.therefrom to cause said thermocouple to generate an electromotive force, the heat not being carried away therefrom by the medium surrounding said one junction when the liquid level is below said predetermined normal level, and means responsive to the electromotive force generated by said thermocouple for controlling said boiler.

9. A liquid level responsive device comprising in combination, a thermocouple having first and second junctions, heating means for said junctions, said heating means tending to heat said first junction to the same or higher temperature than said second junction, a liquid container, and means supporting said first junction so as to be in good thermal conductive relation with said liquid when said liquid is at or above a predetermined level and poor thermal conductive relation therewith when said liquid is below said predetermined level, said second junction being continuously in poor thermal conductive relation to level and said temperatures are substantially the same when said liquid is below said predetermined level.

HUBERT T. SPARROW. 

